Accelerators of vulcanization



Patented Sept. 12, 1950 ACCELERATORS :OF VULOANTZA'TION Albert F. Hardman, Akron, Ohio, assignor to Win-gfoot Corporation, Akron, Ohio, a corporation of Delaware -No Drawing. Application September 17, 1945, Serial No. 616.966

This invention relates to the use of the methylol esters of dithiocarboxylic acids as accelerators of the vulcanization of rubber. These new compounds and their preparation are claimed in my copending application Serial No. 508,404, filed October 30, 1943, now abandoned.

The acids from which the new compounds are formed are dithiocarboxylic acids (RCSSH) in which the acid group (-CSSI-I) is directly connected with a carbon of the acid residue (R.-) Ordinarily, this residue will be a hydrocarbon radical although this is not necessarily the case. The dithiocarboxylic acids include, for example, dithiofuroic acid; dithionaphthoic acid; hydroxy dithionaphthoic acids, such as 2-hydroxy-l-dithionaphthoic acid and l-hydroxy-Z- dithionaphthoic acid, etc.; dithioacetic acid; di-- thiobenzoic acid, etc. The methylol esters may be formed by treating the free dithiocarboxylic acid with formaldehyde or by treating a salt of the acid with formaldehyde in acid solution. The following examples illustrate the production of these new compounds:

The aqueous ammonium dithiofuroate was slowly stirred into a mixture of the hydrochloric acid, formaldehyde, water, and ice. In a few minutes crystals separated. After standing onehalf hour, the precipitate was filtered and washed with cold water. It was. the desired methylol dithiofuroate. I

EXAMPLE 2 Crude disodium-2-hydroxy-1-dithionaphthoate in 200 cc. water g 35 Concentrated HCl cc 20 Formaldehyde (37%) g Water 00.. 400

The aqueous solution of the dithionaphthoate was slowly stirred into a solution of the formaldehyde, acid, and water at .room temperature. Orange-colored crystals separated at once. After standing several hours, the solution was filtered,

and f the precipitate of the methylol-Z-hydroxyl-dithionaphthoate was washed with water.

The eflicacy of the accelerators is illustrated by the following example.

. 2 The product of Example 2 was tested in natural rubber as follows:

Rubber 100.0

Sulfur 3.0

Zinc oxide 5.0

Accelerator 0.5

After curing minutes at 240 C., on test it showed a tensile of 171 kg./sq. cm.; 790 per cent elongation on a modulus of 14 at 300 per cent elongation. 1

In additionto natural rubber, various synthetic rubber-like materials which are similarly vulcanizable may also be used and, for the purposes of this invention, are to be considered as equivalent of natural rubber. This is illustrated by the following example.

The product of Example 1 was tested in a rubber-like copolymer of styrene and butadiene, such as is now known as GR'S, in the following formula:

GR-S 100.0 Sulfur 2.0 Zinc oxide 5.0 Carbon black 40.0 Accelerator 1.0

On curing for 50 minutes at 260 C., a test gave a tensile strength of 141 kg./sq. cm., 465 per cent elongation and a modulus of 117 at 300 per cent elongation.

' It is to be understood that the examples are merely illustrative. The amount of sulfur and accelerator, etc., may be changed, and the compositions may be otherwise varied.

This application is a continuation-in-part of I REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,238,331 Lichty Apr. 15, 1941 2,469,824 I-Iardman May 10, 1949 

1. A METHOD OF TREATING RUBBER WHICH COMPRISES VULCANIZING IT IN THE PRESENCE OF SULFUR AND, AS AN ACCELERATOR, A SMALL AMOUNT OF THE METHYLOL ESTER OF DITHIOFUROIC ACID. 